Backlight-type liquid-crystal displays with a built-in light source therein have been much popularized. Of such backlight-type built-in light sources, a typical structure of an underlight-type backlight comprises a housing 11 that serves both as a profile case and as a light reflector, a diffuser sheet 14, and a light source such as a cold-cathode lamp 15, as in FIG. 2. A typical structure of a sidelight-type backlight comprises a light waveguide with a dot print 12 on a transparent acrylic plate 13, a light reflector 11, a diffuser sheet 14, and a light source such as a cold-cathode lamp 15, as in FIG. 3. In these, the light from the light source is reflected on the light reflector, and forms uniform planar light though the diffuser. Recently, some improvements have been made in these by increasing the power of the lighting source and by increasing the number of the light source lamps therein. For increasing the brightness of these devices with upsizing of displays, plural light sources may be disposed, as in FIG. 2 and FIG. 3.
Heretofore, white polyester films have been much used for the light reflector for the application as herein (e.g., JP-A 4-239540). However, a light reflector that comprises a white polyester film is often problematic in point of its discoloration (yellowing) owing to the recent increase in the quantity of light and to the increase in the ambient temperature by the heat from lamp, and materials that are less discolored have become desired.
Recently, therefore, a light reflector comprising a white polyolefin film has been proposed (e.g., JP-A 6-298957, 2002-31704). In addition, a white polyolefin film has also been proposed, of which the discoloration is smaller than a light reflector comprising a white polyester film (e.g., JP-A 8-262208, 2003-176367). These days, however, there is increasing a demand for further increase in brightness with the tendency toward large-sized displays, and the conventional white polyester films and white polyolefin films are now unsatisfactory. Accordingly, light reflectors having higher brightness and higher reflectivity are desired.